1. Field of the Invention
The present is generally related to an exhaust system for a marine vessel and, more particularly, to an improved system in which the direction of the exhaust is controlled as a function of a preselected parameter or parameters in combination with a noise measurement.
2. Description of the Prior Art
In the field of marine propulsion systems, it is well known that the exhaust from an inboard engine of a marine propulsion system can be optionally directed to an underwater outlet or an above water outlet or partially to both above water and underwater outlets. It is also well known to those skilled in the art of marine propulsion systems that underwater outlets of exhaust gases from an internal combustion engine can reduce the overall noise level emanating from the marine vessel. However, exhausting the gases from an internal combustion engine under water results in increased resistance to the flow of exhaust gases when compared to exhausting these gases at a point above the water level. Therefore, more power can be achieved by an engine in a marine vessel if the exhaust gases are not directed to an underwater outlet.
U.S. Pat. No. 4,773,215, which issued to Winberg et al on Sep. 27, 1988, discloses an exhaust control assembly for a marine stern drive system. The stem drive marine propulsion system has an inboard engine with an exhaust, an outboard drive unit operative coupled to the engine, and separated therefrom by a transom having two exhaust passages therethrough, and an exhaust control assembly aft of the engine exhaust and forward of the transom and within the boat. The assembly has an inlet connected to the engine exhaust, and has first and second outlets communicating with the respective exhaust passages extending aft through the transom. A valve in the assembly selectively controls communication of the inlet with the first outlet.
U.S. Pat. No. 4,995,233, which issued to Lulloff on Feb. 26, 1991, discloses an automatically controlled exhaust assembly for a marine stern drive system. The stem drive marine propulsion system has an inboard engine with an exhaust, an outboard drive unit and a propeller operatively coupled to the engine and separated therefrom by a transom having two exhaust passages therethrough and an exhaust control assembly having an inlet connected to the engine exhaust, first and second outlets communicating with respective exhaust passages extending aft through the transom, and a valve in the assembly having a first condition providing communication of the inlet with the first outlet and a second condition blocking communication of the inlet with the first outlet. Automatic control circuitry automatically controls actuation of the valve between the first and second conditions in response to a given parameter.
U.S. Pat. No. 4,002,136, which issued to Michalak on Jan. 11, 1977, describes a marine exhaust system. The system is intended for use on boats powered by an internal combustion engine. An exhaust chamber is located in the stern of the boat and is connected to the engine exhaust manifold. A submerged exhaust port emits exhaust gases below the water level to silence exhaust noise. The exhaust port has a recessed opening so that relative movement of water past the port assists in drawing the exhaust gases from the chamber. Atmospheric vent holes communicate the chamber with atmosphere to exhaust gases when the boat is idling or operating at slow speeds.
U.S. Pat. No. 4,586,908, which issued to Schlichthorst on May 6, 1986, describes an exhaust gas system for internal combustion engines of a ship. The exhaust gas system for a ship has at least one internal combustion engine for moving the ship through water. The exhaust gas system includes a first gas passage for conducting engine exhaust gases below the water surface and a second gas passage for conducting the engine exhaust gases above the water surface. It also includes a control valve responsive to the position of the ship in the water for determining the selection of the first gas passage or the second gas passage to conduct the exhaust gases, with a cooling member provided for the gases conducted by the first passage and having openings to the water for aspirating or passing the water through the cooling member when the ship moves through the water.
U.S. Pat. No. 5,421,756, which issued to Hayasaka on Jun. 6, 1995, describes an exhaust system for a marine propulsion machine. The exhaust gas discharge system is used on a watercraft and has a first discharge path including a first outlet primarily for use during high speed vessel operation and a second discharge path including a second outlet for use during both low and high speed vessel operation. The first outlet is arranged to constantly remain below a water surface level of a body of water in which the watercraft is operated while the second outlet is arranged to locate above the water level surface during high speed vessel operation and below the water surface at a level higher than the first outlet during idle and low speed vessel operation. Additionally, the second discharge path has an exhaust flow sectional area of a size at least as large as the exhaust flow sectional area of the first discharge path. The system is capable of discharging exhaust gases in a smooth, efficient manner, and is comprised of a relatively simple structure.
When exhaust gases are discharged below the water level of a body of water in which a marine vessel is operated, it is known that the gases can be exhausted through the propeller of the marine vessel. U.S. Pat. No. 5,470,263, which issued to Griffiths et al on Nov. 28, 1995, discloses a method and apparatus for improving reverse thrust of a marine drive. The marine drive has a reverse thrust cup on the propeller shaft between the propeller hub and the rear retaining nut. The reverse thrust cup permits the propeller hub to slide on the propeller shaft fore and aft. When the marine drive is in the forward direction the forward thrust of the propeller forces the propeller hub to the forward position thereby directing engine exhaust out the rear of the propeller hub. Conversely, when the marine drive is in the reverse direction, the rearward thrust created by the propeller hub forces the propeller hub to the rearward position thereby directing exhaust out a forward exhaust opening forward of the propeller blades increasing the reverse thrust of the marine drive.
The patents described above are hereby explicitly incorporated by reference in the description of the present invention.
When the exhaust of a marine propulsion system is exhausted directly through a transom of a boat and not toward the optional underwater discharge point, the noise levels created by the marine propulsion system can possibly exceed certain state or local ordinances and, as a result, this type of operation of a marine vessel can subject the vessel operator to fines and penalties if the noise level caused by the marine vessel exceeds the legal limits. In a typical operation of an exhaust diverter, such as that disclosed in U.S. Pat. Nos. 4,773,215 and 4,995,233, the selection between the underwater discharge and the above water discharge is made either manually or as a function of manifold pressure. The selection of an above water discharge of the exhaust can be made without any regard to the noise level that this election causes. As a result, the operator of the marine vessel can possibly be subject to fines or other penalties if the noisier option is manually selected. It would therefore be significantly beneficial if an exhaust system could be provided that controls the exhaust diverter in a way that minimizes the noise level produced by the marine vessel when operated at low speeds, allows increased noise levels at high speeds when the marine vessel is likely to be located away from populated dock areas, and also limits the maximum sound level emanating from the marine vessel regardless of the location of the vessel or its speed.